1. Field of the Invention
The present invention relates to a switch in which switching takes place by pressing a slide longitudinally, and more particularly to a small-sized switch of a so-called mechanically operable type for use chiefly in switching in response to movement of parts in a system.
2. Description of the Prior Art
FIGS. 5 through 8 illustrate a conventional switch of the type described. As shown in FIG. 5, the conventional switch generally comprises a wafer 3 with a pair of terminals 1, 2 projecting from its lower side, a case 4 mounted on the wafer so as to cover an upper opening thereof, and a slide 6 received through a guide hole 5 of the case 4.
A spring contact 7 in the form of a coil spring leads to one of the terminals 1 via a receiving plate 10 of conductive metal having an elongate protuberance 10a for supporting the spring contact 7, while a fixed contact 8 in the form of a clip leads to the other terminal 2. The slide 6 is vertically reciprocably received through the guide hole 5 of the case 4 with its one end abutting against an abutment portion 7a of the spring contact 7 so that the slide 6 is normally urged upwardly by the resilience of the spring contact 7. The wafer 3 is generally in the form of a molded box within which the receiving plate 10 and the fixed contact are disposed. The case 4 is mounted on the opening side of the wafer 3; thus the wafer 3 and the case 4 are unitarized. Consequently, a coil portion 7c of the spring contact 7 is held against the elongate protuberance 10a of the receiving plate 10 by a pair of parallel projections 4d, 4d extending from the top plate 4e of the case 4 toward the wafer 3, with a contact portion 7b of the contact 7 loosely received through the space between the two projections 4d, 4d, and with the opposite end of contact 7 held in predetermined position of the wafer 3.
A mounting portion 4a of the case 4 has in its opposite ends a pair of grooves 4b, 4b in which a pair of projections 3a, 3a formed on opposite ends of the wafer 3 is respectively engageable. Owing to the resilience of the case 4 itself, these two projections 3a, 3a are prevented from removal out of the respective grooves 4b, 4b except when it is factitiously dismounted. Designated at 4f is a mounting hole for use in attaching the switch to a panel, for example, and designated at 5a is a generally rectangular land defining the guide hole 5.
As is apparent from FIG. 6, a lower end or pressing portion 6a of the slide 6 abuts against the abutting portion 7a of the spring contact 7. When the slide 6 is depressed in the direction of an arrow A, the abutting portion 7a is moved to a lower or receiving portion 3b of the wafer 3 commensurately with the amount of movement of the slide 6. At that time, the contact portion 7b of the spring contact 7, which portion is disposed in substantially parallel relation to the pressing portion 6a of the slide 6, is brought into engagement with the contact 8 as the contact portion 7b is slidably gripped by a clip-like portion 8a of the contact 8, thus causing a conductive coupling between the spring contact 7 and the second terminal 2. As a result the circuit has been closed.
When the pressing force is released from the slide 6, the abutting portion 7a of the spring contact 7 is angularly moved in the direction of an arrow B in FIG. 7 by the resilience of the coil portion 7c of the spring contact 7, and the slide 6 returns to its original or upper position in the direction of an arrow C. This returning of the slide 6 causes the abutting portion 7a of the spring contact 7 to return to its original position, thus bringing the contact portion 7b out of contact with the clip portion 8a of the contact 8. As a result the circuit has been opened.
If the thus constructed switch is placed adjacent to one of various movable parts of a system so that the slide 6 is movable in response to movement of the one part, it is possible to detect the position of the one part and then to switch movements of the related parts.
However, the amount of force at which the coil portion 7c of the spring contact 7 is gripped between the projection 4d of the case 4 and the protuberance 10a of the receiving plate 10, must be not so great so as not to impair the resiliency of the coil portion 7c. This type of switch, which is ordinarily very small-sized in connection with the associated parts, is subject to inaccurate positioning of the spring contact 7 due to even a small dimensional error. For this reason, when the slide 6 is depressed to move the abutting portion 7a of the spring contact 7 to the receiving portion 3b of the wafer 3, the coil portion 7c of the spring contact 7 is angularly raised away from the elongated protuberance 10a of the receiving plate 10 in the direction of an arrow D in FIG. 7 with the other end of the spring contact 7 (opposite to the abutting portion 7a and the contact portion 7b) as a fulcrum, thus causing only a poor engagement between the spring contact 7 and the receiving plate 10. With this conventional switch, accurate and reliable switching operation is difficult to achieve.